Snapshot A 22-year-old man presents to his primary physician's office for worsening knee pain. He reports that his symptoms began approximately 1 week ago and has worsened to the point of not being able to bend the knee. He states to being sexually active with multiple partners and inconsistently using condoms. On physical exam, the left knee is erythematous, swollen, and tender to palpation. There is decreased range of motion on the affected joint. Laboratory testing demonstrates an elevated erythrocyte sedimentation rate and C-reactive protein. An athrocentesis is obtained and demonstrates a white blood cell count of 55,000 cells/μL and gram-negative organisms. Empiric antibiotics are administered and orthopedic surgery is consulted. Introduction Clinical definition login to view 4 more bullets Epidemiology login to view 9 more bullets Etiology login to view 11 more bullets Pathogenesis login to view 5 more bullets Prognosis login to view 2 more bullets Presentation Symptoms login to view 2 more bullets Physical exam login to view 6 more bullets Imaging Radiography login to view 2 more bullets Studies Labs login to view 1 more bullet Arthrocentesis login to view 1 more bullet Synovial fluid culture login to view 6 more bullets Differential Gout Pseudogout Inflammatory arthritis (e.g., rheumatoid arthritis) Viral arthritis (e.g., hepatitis B and C and parvovirus B19) Treatment Medical login to view 11 more bullets Operative login to view 8 more bullets Complication Osteomyelitis Sepsis